The conventional colour liquid crystal display includes a liquid crystal layer, and a semi-transparent metal oxide layer (typically Indium Tin Oxide) that covers the liquid crystal layer. These two layers are sandwiched between two transparent substrates, which are typically provided as glass or plastic plates.
In a passive matrix display, one of the transparent substrates includes a series of parallel data electrodes, and the other transparent substrates includes a series of parallel scanning electrodes that are arranged at a right angle to the data electrodes. The pixels are addressed by applying a pulse to the associated data electrode, while grounding the associated scanning electrode.
In an active matrix display, one of the transparent substrates includes a matrix of thin-film transistors and storage capacitors. The display includes a transistor for each pixel in the display. The gate electrodes of the transistors in each row are connected together via a common scanning electrode, and the source electrodes of the transistors in each column are connected to a respective source driver. The pixels can be individually addressed by pulsing the scanning electrodes sequentially, and by applying the appropriate voltage signals to the data lines. The storage capacitors maintain the voltage applied to each pixel until the next voltage signal is applied.
In each case, the optical transmittance of the display changes as the liquid crystal moves in response to the voltage applied to each corresponding section of the metal oxide layer. Therefore, the opacity of each pixel can be controlled via the voltage applied to the scanning and data electrodes.
Cross-talk is a problem experienced with some liquid crystal displays in which the voltage applied to pixels on one part of the display influences the transmittance of the liquid crystal on pixels on other parts of the display. This problem is a result of several factors, including parasitic capacitance between the source and gate lines, and voltage drops due to the resistance of the metal oxide layer. As a result, cross-talk is particularly apparent when the display is rendering an image comprising a large bright (white) area on a dark (black or grey) background, or vice versa. In these cases, the bright area appears to bleed into the dark area, or vice versa.
Attempts have been made to reduce the likelihood of cross-talk occurring on a liquid crystal display. For instance, Howard (U.S. Pat. No. 4,845,482) describes applying gating signals to the scanning electrodes for a shorter than normal interval, applying the data signal to the data electrodes during this shorter interval, and applying a compensation signal to the data electrodes during the remainder of the normal interval.
Choi (U.S. Pat. No. 5,774,103) describes driving the data electrodes from +Vd to −Vd through an intermediate voltage level.
Bitzakidis (U.S. Pat. No. 5,798,740) and Kawamori (U.S. Pat. No. 5,691,739) describe applying a compensation voltage to the data signal applied to each column electrode. Bitzakidis bases the compensation voltage on the capacitance of the transistors and the values for all the pixels in the same column. Kawamori bases the compensation voltage on the number of polarity inversions during each display period.
Bassetti (U.S. Pat. No. 5,670,973) describes applying boost voltages to the row and column electrodes in proportion to the number of ON pixels in a row or column, the number of adjacent ON-OFF and OFF-ON pixel pairs in each column, and the position of each such pixel in each row.
All these implementations require modifications to the display drive circuitry or the glass patterning mask tooling.
Murata (US 2004/0239587) describes, for each scan line, determining the average pixel value for the scan line, and then, for each pixel on the scan line, calculating the difference between each pixel value and the calculated average. The difference figures are input into a correction level determining unit that generates correction values based on the difference figures and a non-linear correction function. The correction values are then input into a correction unit that adjusts the value of each pixel based on the corresponding correction value.
FIG. 6 of the patent application depicts a white box surrounded by gray space, and the adjusted pixel values for each pixel on the scan line. As shown, for the line A-A′ passing through the white box, the pixel values for the gray space to the left and right of the white box are increased by the correction value (α), while the pixel values for the white box remain unchanged. However, for the line B-B′ extending through the gray space below the white box, the pixel values for the entire line remain unchanged thereby creating the possibility of a visual discontinuity between the gray space above/below the box and the gray space to the left/right of the box.